Chemistry 110 Bettelheim, Brown, Campbell & Farrell Ninth Edition Introduction to General, Organic and Biochemistry Chapter 19 Carboxylic Anhydrides, Esters & Amides
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Chemistry 110
Bettelheim, Brown, Campbell & FarrellNinth Edition
Introduction to General,
Organic and Biochemistry
Chapter 19
Carboxylic Anhydrides, Esters & Amides
Carboxylic Anhydrides & Esters
The functional group defining these compounds is the Carboxyl Group: Carbonyl + Hydroxyl
The Carboxyl Group is Planar
CO
O120E 109E
Anhydrides, Esters & Amides are derived from Carboxylic Acids.
An anhydride is formed from the condensation of two acids.
C
O
OHRC
O
HO R+ - H2O
C
O
R RO
O
C
An ester is formed from condensation of an acid and an alcohol.
C
O
OHR R'HO+ - H2O
R'OR
O
C
An amide is formed from condensation of an acid and an amide.
C
O
OHR R'HNR''+ - H2O
R'NR''
R
O
C
Only ammonia, 1E and 2E amines will work here! Why?
Anhydrides of Carboxylic AcidsThe functional group of an anhydrideanhydride is two carbonyl (acyl)
groups bonded to the same oxygen atom.The anhydride may be symmetrical (from two identical acyl
groups), or mixed (from two different acyl groups). However the symmetrical ones are the most common.
To name an anhydride, drop the word "acidacid" from the name of the carboxylic acid from which the anhydride is derived and add the word "anhydrideanhydride“.
CO
OOC
CO
OH CO
HO H2OA powerful dessicantmust be used here!
Anhydrides are very reactive and are produced as reagents.
Benzoic anhydride
Esters - RC(O)OR’Esters have an alkyl group bonded to the carboxylate group.
The group is polar but unlike carboxylic acids it cannot donate a hydrogen bond to itself.
Esters are more volatile (lower boiling) than carboxylic acids and are somewhat less soluble in water than carboxylic acids of similar molecular weight.
Esters have pleasant, fruity odors and most are nontoxic.
They are also unsaturated and undergo many reactions with polar molecules.
A cyclic ester is called a lactone.
δ+
δ-
R
C
O
C O
estergroup is planar
Naming Esters –Common & IUPAC
CH3COCH3
O
CH3OCCH2CH3
O
CH3CH2COCH2CH3
O
CH3CH2CH2COCH3
O
Common Name IUPAC Name
OCCH3
O
methyl acetate methyl ethanoate
methyl propionate methyl propanoate
ethyl propionate ethyl propanoate
methyl butyrate methyl butanoate
phenyl acetate phenyl ethanoate
For smaller esters the common names are most often used!
IUPAC Name the following Esters
CH3CHCH2CH2CH2COCH3
CH3 O
OCCH2CH3
O
CH2CH2OCCH3
O
COCH3
O
COO
Look for the alcohol (alkoxy) part, name it using -yl.
Look for the carboxylic acid (acyl) part, name it using -ate.
Synthesis of Esters & Acyl Transfer AgentsFischer esterification:
+ H2OCH3C
O
OHacyl group
+ OCH2CH3H H CH3C
O
OCH2CH3
alcohol group alcohol group acyl group
This reaction can be driven by removing (adding) water or by adding excess alcohol or acid, Le Chatelier’s Principle.
Acyl group transfer reactions:
acid chloride + HClCH3C
O
Clacyl group
+ OCH2CH3H CH3C
O
OCH2CH3alcohol group alcohol group acyl group
100%
acid anhydride
CH3C
O
OCCH3
O+
acyl group
OCH2CH3H CH3C
O
OCH2CH3
alcohol group alcohol group acyl group
100%+ HOCCH3
O
Mechanism of Fischer Esterification
alcoholcarboxylic acid
CH3CH2C
O
O
CH3
CH3CHester
CH3CH2C
O
OH
acid catalystH
CH3CH2C
O
OH
H
CHCH3
CH3
O
H
CHCH3
CH3
O
CH3CH2C
OO
HH
H
CH3CH2C
O
OH
H
H
CHCH3
CH3
O
Hydrolysis (Breakdown) of EstersHydrolysis - Reverse of Fischer esterification:
carboxylic acid
+ OCH2CH3Halcohol group
CH3C
O
OCH2CH3
alcohol group acyl group
HOH+ CH3C
O
OHacyl group
H2OH
excessalcohol
Saponification:
Long unbranched carboxylate group = "Soap"
+CH3C
O
OCH2CH3alcohol group acyl group
+NaOH OCH2CH3Halcohol group acyl group
CH3C
OONa
This reaction goes in 100% yield if equimolar base is used. Saponification is a reference to use of this reaction in making soap.
Mechanism of Saponification of Esters
CH3CH2CO
esterHO CH
CH3
CH3
OCH3CH2C
O
OH
CH3
CH
CH3
O
CH3CH2CO
O H
CH3
CH
CH3
O+
carboxylate anion alcohol
CH3CH2CO
OCH
CH3
CH3
O
H
AmidesThe functional group of an amideamide is a carbonyl group bonded
to a nitrogen atom.To name an amide, drop the suffix -oicoic acidacid from the IUPAC
name of the parent acid, or -icic acidacid from its common name, and add –amide.amide.
if the amide nitrogen is bonded to an alkyl or aryl group, name the group and show its location on nitrogen by N- ; two alkyl or aryl groups by N,N-di- .
Cyclic amides are called lactams.
* amide linkage
Amides:
N-alkyl N,N-dialkyl
C NR2
OC NHR
O
C NH2
O
* *
N
O
H
lactam
*
Properties of AmidesAmides are polar, hydrogen bond with water, and each other
when the nitrogen bears a hydrogen atom.
Amides have much higher melting and boiling points than alcohols or amines of similar molecular weight, are also solublein water if the substituent group part is not too large and non-polar.
Amides do NOT affect the pH of a water solution.
The amide linkage can be hydrolysed in strong acid or base solution.
CHCH3
CH3
NH
O
CH3CH2Cacyl part
amine part
amide linkage
Acid hydrolysis gives a carboxylic acid and an ammonium salt.
Base hydrolysis gives the carboxylate salt and an amine.
Why does one get the last two results?
Name these Amides
C NH2
OCH3 C NHCH3
OCH3 C N(CH3)2
OCH3
CH3CH2CHCNHC6H5
O
CH3
C NH
CH3
O
The common names are most commonly used here.
The IUPAC names would probably be used with these.
Synthesis of Amides with Acyl Transfer Agentsacid anhydride
+ HOCCH3
O
CH3C
O
OCCH3
O
+acyl group
NCH2CH3H
CH3
CH3C
O
NCH2CH3
CH3
amine group amine group acyl group
100%
acid chloride
+ HCl
CH3C
O
Clacyl group
+ NCH2CH3H
CH3
CH3C
O
NCH2CH3
CH3
amine group amine group acyl group
100%
These methods are most commonly used, requiring little heat.
Carboxylic Acids & Amines Give SaltsA carboxylic acid and an amine react as acid and base to form a salt:
The acyl transfer reaction does not occur unless the salt is heated strongly. Many reactions fail because of excess heat.
+ NCH2CH3H
CH3
H amine group
CH3C
O
OHacyl group
+ NCH2CH3H
CH3
amine group
100%
acyl group
CH3C
O
O
+ NCH2CH3H
CH3
H amine groupacyl group
CH3C
O
O HeatStrongly
amine groupacyl group
CH3C
O CH3
NCH2CH3
+ H2O
Acids & Bases Hydrolyze Amides
carboxylic acid
strong acid
ammonium salt
+
one mole
Cl
CHCH3
CH3
N
HH
H
CH3CH2C
O
OH
CHCH3
CH3
NH
H
OHH
Cl
water
CH3CH2C
O
Hydrolysis of amides requires one mole of acid (base) and one mole of water, using more rigorous conditions than for esters.
one mole
CHCH3
CH3
NH
sodium hydroxide
Na OH
CH3CH2C
O
+Na
carboxylate anion
CH3CH2C
O
O
amine
CHCH3
CH3
NH
H
Complete these hydrolysis reactions.
N C CH2CH3
O
N C CH2CH3
O
HClH2O
NaOHH2O
Esters & Anhydrides of Phosphoric Acid
P
O
HOOH
OHP
O
O
O
PO
O
PHO
OH OH OHOH
Phosphoric Acid
Diphosphoric Acid
Triphosphoric Acid
P
O
O
O
PHOHO OH
OH
Polyphosphoric acids form from condensation reactions
Removing onemolecule of H 20
from two molecules of phosphoric acid.
A phosphoric anhydridehas two phosphoryl groupsbonded to the same oxygen.
H3PO4+H2O
Each of the hydroxyl groups is acidic and form anionsjust above pH = 7.
P
O
O
O
P-O-O O-
O-Phosphoric acids can form esters with alcohols at any(all) hydroxyl groups butmono and di-esters aremost important in biology.
P
O
O
O
PHOHO OH
OR
+ ROH- H2O
Phosphoric Acid Mono-ester Ionization
ROPOH
O
OH
ROPOH
O
O
ROPO
O
O
diprotic acidfavored at low pH
singly ionizedfavored at pH just below pH = 7
doubly ionizedfavored at pH > 7
Phosphate esters’ solubility is affected by the pH of the solution. A solubility switch, as well as a buffering action isoperating in physiologic fluids. Phosphate esters can donate hydrogen ions if the pH goes too high, can accept hydrogen
ions if the pH goes too low.
Formation of Phosphate Ester Anhydrides
Di- and Tri-Phosphates Can only be formed or broken-down in physiologic fluids in the
presence of an enzyme. These molecules serve as energy storage species in physiology.
ROPOH
O
OHROPOPOH
O O
OHHO
ROPOPOPOH
O
OH
O O
OHHOHOPOH
O
OH
enzyme
H2O
HOPOHO
OH
enzyme
H2O
Mono-Esters of Diphosphoric and Triphosphoric Acid
Break-down of Phosphate Ester Anhydrides
ROPOH
O
OH
ROPOPOH
O O
OHHOROPOPOPOH
O
OH
O O
OHHO
ROH
enzyme
ROH
enzyme++
ROPOH
O
OH
ROPOH
O
OH
Alcohol-olysis of Esters of Diphosphoric and Triphosphoric Acid
Adenosine Di- and Triphosphate
Power Cells in Physiology
Adenosine Diphosphate
ADP
Adenosine Triphosphate
ATP
HOPOHO
OHenzyme
H2OOPOPOPO
O
O
O O
OO
CH2
N
N
N
N
NH2
OHOH
OOPOPO
O O
OO
CH2
N
N
N
N
NH2
OHOH
O
Step-Growth PolymersStepStep--growth polymersgrowth polymers are formed by reaction between
molecules containing two functional groups, with each new bond created in a separate step.
We will discuss three types of step-growth polymers: polyamides, polyesters, and polycarbonates.
-H2 O+
Hexanedioic acid(Adipic acid)
1,6-Hexanediamine(Hexamethylenediamine)
heat
n
Nylon-66(a polyamide)
O
HO OHO
N N
ON
ON
H
HH
Hremove H2O
H
H
Polyamides:
Nylon 66 was the first purely synthetic fiber, a synthetic “silk”.
Step-Growth PolymersPolyamides:
COHnHOCO O
N NH
HH
H
NHCNHCO O
-H2 O
1,4-Benzenediamine(p-Phenylenediamine)
1,4-Benzenedicarboxylicacid
(Terephthalic acid)
nKevlar
(a polyaromatic amide)
+ heat
remove H2O
The polyaromatic amide known as KevlarKevlar is made from an aromatic dicarboxylic acid and an aromatic diamine
As many of you know from news reports this is the material used in “bullet-proof”vests and soldiers’ helments.
Step-Growth PolymersPolyesters:
OCH3
OCH3 O
O HO
OH
O
O
OO
-CH3 OH
Poly(ethylene terephthalate)(Dacron, Mylar)
heat
n
1,2-Ethanediol(Ethylene glycol)
Dimethyl terephthalate
+
remove CH3OH
The first polyester, now called PET (polyethylene terephthalate) has many uses, one is clear soft-drink bottles.
This reaction, a trans-esterification displaces the small molecule methanol to form a polymeric condensation product.
Step-Growth PolymersPolycarbonates:
This polycarbonate is most polycarbonate is most familiar asfamiliar as Lexan, used in clear plastic castings, “shatter-proof glass” and airplane canopies.
+ Na-OCH3
CH3
O- Na+ Cl Cl
O
OCH3
CH3
O
O
-NaCl
P hosgen e
+
Disodium salt of Bisphenol A
Lexan(a p olycarbonate)
n
remove Na+Cl-
This reaction, a metathesis, removes the elements of a salt fromthe bisphenol and from the diacid chloride of carbonic acid.
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